Combined wastewater treatment and power generation

ABSTRACT

Both apparatus and a method for the treatment of domestic wastewater are described. A substantial reduction in refractory nutrient content of such waters is effected by the addition of an electrolyte, if needed, and passage of the wastewater through battery-cell structure having as one electrode thereof a metal the oxide of which, when formed in water, acts as a flocculent. Air introduced into the cell prevents suspended sludge from settling in the cell and provides (or supplements) the depolarizing oxidant. Conduct of the process simultaneously produces direct current electrical power, as well, which may be employed to release chlorine from an aqueous chloride solution for combating pathogenic organisms in the wastewater.

Unite States Patent Setser et a1.

[451 Jan. 18, 1972 COMBINED WASTEWATER TREATMENT AND POWER GENERATION[72] Inventors: James L. Setser, Schenectady; Eugene P.

Schneider, Jr., Webster, both of NY.

3,359,136 12/1967 Merten et al.. ...l36/86 A 3,421,994 1/1969 Le Duc136/86 X 3,432,358 3/1969 ....l36/86 3,457,115 7/1969 ....l36/863,497,388 2/1970 Weissman ..l36/86 X All? FOREIGN PATENTS ORAPPLICATIONS 206,350 1/1909 Germany ..l36/86A 259,654 1/1968 Austria..l36/86 Primary ExaminerAllen B. Curtis Attorney-Richard R. Brainard,Paul A. Frank, Charles T. Watts, Leo I. Malossi, Frank L. Neuhauser,Oscar B. Waddell and Melvin M. Goldenberg [57] ABSTRACT Both apparatusand a method for the treatment of domestic wastewater are described. Asubstantial reduction in refractory nutrient content of such waters iseffected by the addition of an electrolyte, if needed, and passage ofthe wastewater through battery-cell structure having as one electrodethereof a metal the oxide of which, when formed in water, acts as aflocculent. Air introduced into the cell prevents suspended sludge fromsettling in the cell and provides (or supplements) the depolarizingoxidant. Conduct of the process simultaneously produces direct currentelectrical power, as well, which may be employed to release chlorinefrom an aqueous chloride solution for combating pathogenic organisms inthe wastewater.

6 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION In general, theobject in treating domestic and/or industrial wastes containingpollutional materials (hereinafter called sewage or wastewater) is toremove soluble nutrients and this is usually accomplished by thecombination of biological oxidation and conversion of such nutrients tocellular material. Usually, waste treatment involves the steps of (a)settling the sewage to remove solids of large particle size, (b)subjecting the effluent from the settling tanks to some aerobic oranaerobic biological treatment, separating the cell mass producedthereby from the liquid medium and (d) discharging the liquid medium forultimate reuse. With respect to the aerobic biological treatment, thisprocess step is generally either the trickling filtration method or theactivated sludge method, though many modifications of these methods havebeen developed and utilized.

Such biological contact methods liberate the mineral constituents oforganic matter to the wastewater. As a result large quantities ofminerals are discharged daily in sewage effluent causing the pollutionof lakes, streams and estuaries and cansing fertilization of thereceiving waters which promotes undesirable blooms in aquaticvegetation, particularly unicellular algae. Such blooms are unsightlyand produce such obnoxious odors on decaying as to prevent recreationaluse of the water and may even be toxic to aquatic life, wild life anddomestic animals;

The art is, therefore, in need of economically feasible wastewatertreatment methods and apparatus developed to eliminate or reduce thequantity of carbon, nitrogen and phosphorous nutrients discharged withwaste-water treatment effluents.

SUMMARY OF THE INVENTION One effective response to this demand in theart is provided by the instant invention in which wastewater to which anelectrolyte has been added if necessary, is passed through an electricalpower source consisting of (a) an air electrode; (b) an electropositiveanode made of a metal productive of an oxide which, when formed inwater, acts as a flocculent; (c) means for introducing a stream of airinto the device to float flocculated sludge formed during the process sothat liquid flow will carry this suspended flocculated material out ofthe cell, and (d) collecting means wherein the suspended material cansettle. The preferred embodiment of this invention employs magnesium asthe metal anode and an electrode structure on an electronicallyconductive grid comprising (a) a hydrophilic binder (b) electronicallyconductive, catalytically active carbon particles held together by thebinder and (c) a hydrophobic impregnating material.

The term air electrode" is used in the conventional sense as meaning anelectrode which is capable of electrochemically reducing oxygen fromambient air.

The general construction features of the gas-depolarized electricalpower unit and of a preferred activated carbon electrode constructionare disclosed in US. applications Ser. No. 511,392 Kent, (now US. Pat.No. 3,457,1 l5) filed Dec. 3, 1965 and Ser. No. 664,366 Moran et al.filed Aug. 30, 1967, respectively, and both the aforementionedapplications are incorporated herein by reference. Both theaforementioned applications are assigned to the assignee of the instantapplication. As may be seen in comparing the instant invention with thecell structures in the Kent and Moran et al. applications, the filterhas been eliminated from around the anode.

BRIEF DESCRIPTION OF THE DRAWING The nature of this invention as well asobjects and advantages thereof will be readily apparent fromconsideration of the following specification relating to the annexeddrawing in which:

FIG. l is a three dimensional, cutaway view schematically illustratingthe simplest structure for the conduct of the instant invention and FIG.2 is a cross-sectional view through a modified cell showing essentialcomponents having counterparts in the structure of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The wastewater treatment cell 10comprises a longitudinally extending casing 11 having as the major facesthereof the air electrodes 12 and 13. The electropositive metal plate 14is disposed between air electrodes 12 and 13 to separate casing 111 intotwo longitudinally extending compartments between plate 14 and airelectrode 12 spaced therefrom, on the one hand, and plate 14 and airelectrode 13 spaced therefrom, on the other. These compartments aredesignated by the numerals 16, 17.

Input to the cell may, for example, be digester liquor to which it isdesired to apply tertiary treatment or may be raw sewage in which caseit is first mascerated to produce fine suspended solids in the flow.wastewater supply conduit 18 connects with both chamber 16 and chamber17 to admit wastewater thereto. Air is introduced via lines 19 and 21into these same compartments via sparger pipes 22, 23 extending alongthe bottom of compartment 16 and 17. The treated wastewater leaves cell10 via outlet 24 in communication with each compartment 16, 17 and intoa sump 26 where the flocculated sludge 27 settles. Electrolyte from asource not shown is metered into the wastewater flow via inlet 18, ifrequired.

Electrodes 12 and 13 may be made in the manner disclosed in either ofthe aforementioned applications Ser. Nos. 51 1,392 and 664,366 in whichcase air may enter cell 10 through walls 12 and 13, but the liquidcontained in the cell cannot leak out. However, if preferred, these cellwalls may be of nonporous block carbon and full reliance for oxygen toelectrodes 12, 13 is then placed on the airflow via lines 19, 21. Thus,the sole criterion for electrodes 12 and 13 is that they be gasdepolarizing, which means that molecules of oxygen coming into contacttherewith are reduced electrochemically to the ionic state. These oxygenions then react with the ions of the anode metal, which dissolve intosolution, because of the electropositive nature of the metal. The metalion and oxygen ion combined in aqueous solution to form a metal oxidehydrate flocculent. This flocculent entraps fine solid matter suspendedin the wastewater to bring about precipitation thereof. However, theprecipitation of the flocculated matter in the cell itself is preventedby (a) the constant introduction of air via spargers 22, 23 and (b) thehydrogen gas evolvement, which occurs simultaneously in the cell.

Magnesium, aluminum and zinc are electropositive metal anode materialsuseful with-gas depolarizing electrodes for the production of flocculentso necessary to the practice of this in vention. The following reactionsappear to be among those occurring in the cell using the magnesiumanode:

Magnesium Anode Reaction: Mg+20I-I'' Mg(OH) +2e Cathode Reaction: ll/20+H O+2e'- 20H- The electrochemical mechanisms occurring are complex andare not completely understood, however, experimental observations verifythat beneficiation of the sewage and the generation of useful current dooccur. In addition in each case electrolysis of water providescontinuous hydrogen evolvement.

Although the metal anode would be construed predominately of the primeelectrochemically active ingredient, such as magnesium, aluminum or zincas noted above, it is conventional for significant amounts of othermetals to be present as well, for example, commercially availablemagnesium anodes typically employed in excess of percent by weightmagnesium with the remaining material being principally aluminum andzinc. Additional anode ingredients may also be present to controlcoulombic efficiency, voltage,

protect against parasitic attack or may merely be present as impurities.Slots-29, 31 readily accommodate the removal and replacement of metalanode 14 as required.

For handling larger capacity wastewater flows several such cells can beplaced adjacent each other and, if gas permeable wall electrodes areemployed, air may also be admitted between cells.

Although the most convenient method of introducing electrolyte to thesystem is in the form of sodium chloride or brine, other salts mayequally well serve as electrolytes, as for example, calcium sulfate orother salts present in brackish water.

Direct current power generated during wastewater treatment is availableat terminals 32, 33, which power may be applied to many uses, forexample, in the decomposition of an aqueous chloride solution to releasechlorine gas, which may be admitted to cell 10, to sump 26 or theoutflow from sump 26 for residual killing power to combat pathogens.

Also, the flocculated sludge accumulating in sump 26 may be removed andpumped via pump 34 either to a primary flocculating tank, not shown, forpretreatment of the raw sewage or to apparatus for disposition thereofby filtration and incineration.

The conduit 40 shown in FIG. 2 is a modified version of the cell 10. Theexterior wall 41 is an air electrode and centrally located anode rod 42provides the electropositive metal. Preferably air would be admitted tothe device via sparger 43 although air could be admitted through theexterior wall 41 at separated points to insure sufficient flotationmedium for suspending the floc generated in the system. Spider 44, whichsupports anode rod 42, is loose so that by disconnecting lengths ofconduit 40 the depleted rods 42 may be removed and replaced.

This invention may be practiced either as a batch process or as acontinuous process. Examples l-1 1 set forth herein below are examplesof batch treatment of wastewater or digestor liquor, while succeedingexamples illustrate the application of this invention to continuoustreatment. Hydrogen gas was EXAMPLE 1 340 ml. of settled wastewater wereintroduced to cell 10. This wastewater has a COD of 216 mg./1. and a pHof 7.56 mixed with NaCl to give a salt concentration of 1,000 ppm. NaCl.

1. Reaction time 8 minutes 2. After reaction-color clear 3. Afterreaction-odor none 4. After reactiongrey flocculant 5. After reactionCOD86 mg./ 1.

6. After reaction-pH 10.10

EXAMPLE 2 Several samples (340 ml.) of settled wastewater having aninitial COD of 185 mg./l. were introduced into cell 10 to determine theeffect of electrolyte addition:

Salt Concentration Sample (p.p.m.) COD (mg/1.) pH

- In examples 1 and 2 the treatment time was 8 minutes and the currentoutput was 1.3 amperes.

EXAMPLES 3-1 1 A. Test Conditions Example 3-340 ml. sample of digestorliquor treated for 1 mm. I

Example 4-340 ml. sample for 1.5 min.

Example 5-340 ml. sample for 2 min.

Example 6340 ml. sample for 3 min.

Example 7-340 ml. sample for 5 min.

Example 8-340 ml. sample for 6 min.

Example 9-340 ml. sample for 4 min.

Example l0-340 ml. sample for 8 min.

Example 1 l-340 ml. sample for 12 min. The current output in each casewas fixed at 12.9 milliamps/cm. and the electrolyte was NaCl (1 percentby weight).

(B) ANALYTICAL RESULTS Sample SS TS pH COD NHg-N TN T-PO4 Examples:

3-8 input; 7, 005 11. 60 408 295 510 3 output 0 6, 700 11. 70 312 268490 35 4 output 5 6, 605 11. 75 336 275 490 24 5 output" 3 6, 530 11. 70304 270 486 18 6 output. 0 6, 490 11. 74 300 269 482 5 7 output. 0 6,380 11. 86 324 274 486 8 g tillltputu 5 6, 360 11. 75 320 270 496 11input" 90 7, 105 11. 66 392 279 501 0 output. 0 6, 480 11. 76 306 256472 16 10 output. 0 6, 430 11. 90 295 252 488 11 11 output; 0 6, 300 11.70 292 260 480 10 EXAMPLE 12 Input Output Analysis (mg./l.) (mg./l.)Reduction pH 7.20 9.85 COD 402 68 83.0 BOD, 259 24 87.5 Total Phosphate25 .3 3.2 83.0 Total Nitrogen 42.1 20.5 51.3 Mg 4.3 4.1 Suspended Solids103 15 75.8 Total Solids 579 285 50.8

Total Volatile Solids 400 200 50.0

Salt (NaCl) concentration 1% Current output= 10 amps 12.9 milliamps/cmF)Voltage output 4 volts DC Vol. ofcell 400 ml.

Flow rate 100 mL/min. of premacerated raw sewage From the data set forthhereinabove it may be concluded that the parameters reflecting change inrefractory nutrient content (COD, BOD T-P, T-N and SS) have beensignificantly reduced indicating that there has been a substantialupgrading of the quality of the effluent in each case. Significantelectrical energy was generated during the battery operation, forexample, in example 12 the direct current power generated would beenough to oxidize chloride ions to chlorine gas. Hydrogen gas evolvedduring the process may be discarded, if desired, but may be collected,dried and used as a fuel supplement for sludge incineration.

1t is to be understood that the several electrode structures shownschematically in FIGS. 1 and 2 are mounted in electrically insulatedrelationship to each other and that where flows of air or wastewatermust be forcefully moved, pumps not shown, will be employed.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. Apparatus for the simultaneous treatment of wastewater and powergeneration comprising in combination:

a. a compartment defined in part by two spaced longitudinally extendingwalls supported in electrically insulated relationship,

b. one of said walls being made of an electropositive metal the oxide ofwhich, when formed in water, acts as a floc- 5 culent,

c. the other of said walls being-an air electrode,

d. means connected to said compartment from a source of wastewater forintroducing wastewater flow into said compartment for passage betweensaid walls,

e. means for admitting a'flow of air into said compartment between saidwalls,

f. means connected to said compartment for conducting treated water flowcontaining suspended flocculated solids out of said compartment aftertransit thereof between said walls,

g. means for receiving said treated water flow for the separation offlocculated solids therefrom and h. first and second electrode meanselectrically connected to said air electrode and said electropositivemetal, said electrode means being adapted to be connected to an externalelectrical load.

2. The apparatus for the simultaneous treatment of wastewater and powergeneration as recited in claim 1 wherein the electropositive metal isselected from the group consisting of magnesium, zinc and aluminum.

3. Apparatus for the simultaneous treatment of wastewater and powergeneration comprising in combination:

d. meansextending along said COX'ldUJit means for admitting a flow ofair into the wastewater flow and e. first and second electrode meanselectrically connected to said air electrode and said rod ofelectropositive metal, said electrode means being adapted to beconnected to an external electrical load.

4. The apparatus for the simultaneous treatment of wastewater and powergeneration as recited in claim 3 wherein the electropositive metal isselected from the group consisting of magnesium, zinc and aluminum.

5. A method for reducing the refractory nutrient content of wastewatercomprising the steps of:

a. adding electrolyte to wastewater to be treated,

b. passing said wastewater between and in contact with spacedlongitudinally extending, first and second electrodes mounted inelectrically insulated relationship, said first electrode being an airelectrode and said second electrode being made of an electropositivemetal the oxide of which, when formed in water, acts as a flocculent,

c. connecting said electrodes to an external electrical load for theapplication thereto of useful power generated,

d. simultaneously flowing air into the wastewater between saidelectrodes to float the flocculent generated and its refractory nutrientcontent,

e. conducting said treated wastewater and suspended flocculent tocollecting means wherein the suspended flocculent can settle and I f.recovering said treated wastewater substantially free of flocculent.

6. The method for reducing the refractory nutrient content of wastewateras recited in claim 5 wherein power generated is used to decompose anaqueous chloride solution for the generation of chlorine gas.

2. The apparatus for the simultaneous treatment of wastewater and powergeneration as recited in claim 1 wherein the electropositive metal isselected from the group consisting of magnesium, zinc and aluminum. 3.Apparatus for the simultaneous treatment of wastewater and powergeneration comprising in combination: a. conduit means having as wallarea thereof an air electrode, said conduit means being in flowcommunication with a source of wastewater, b. an unscreened centrallylocated longitudinally extending rod made of an electropositive metalthe oxide of which, when formed in water, acts as a flocculent, c. meansfor mounting said rod in spaced electrically insulated relationship tosaid air electrode, d. means extending along said conduit means foradmitting a flow of air into the wastewater flow and e. first and secondelectrode means electrically connected to said air electrode and saidrod of electropositive metal, said electrode means being adapted to beconnected to an external electrical load.
 4. The apparatus for thesimultaneous treatment of wastewater and power generation as recited inclaim 3 wherein the electropositive metal is selected from the groupconsisting of magnesium, zinc and aluminum.
 5. A method for reducing therefractory nutrient content of wastewater comprising the steps of: a.adding electrolyte to wastewater to be treated, b. passing saidwastewater between and in contact with spaced longitudinally extending,first and second electrodes mounted in electrically insulatedrelationship, said first electrode being an air electrode and saidsecond electrode being made of an electropositive metal the oxide ofwhich, when formed in water, acts as a flocculent, c. connecting saidelectrodes to an external electrical load for the application thereto ofuseful power generated, d. simultaneously flowing air into thewastewater between said electrodes to float the flocculent generated andits refractory nutrient content, e. conducting said treated wastewaterand suspended flocculent to collecting means wherein the suspendedflocculent can settle and f. recovering said treated wastewatersubstantially free of flocculent.
 6. The method for reducing therefractory nutrient content of wastewater as recited in claim 5 whereinpower generated is used to decompose an aqueous chloride solution forthe generation of chlorine gas.